A technology referred to as a “sensor network” or a “machine to machine (M2M) network” has been and is being developed, in which an information terminal exchanges information or gives an instruction using a communication function. In such a network, a multi-hop communication technology such as typically ZigBee®, in which a terminal itself relays data, has been in practical use because it is easy to set up.
Operations to be performed using communication, for example, include uploading to a server of motion video obtained from a monitoring camera, downloading of content to a video display device placed in public locations, and automatic updating of software data held in an information terminal.
A system referred to as “digital signage” downloads advertising content and other data to a terminal (a digital-signage terminal). It is possible that this digital-signage system is realized by the multi-hop communication technology. In such an example, highly reliable communication is desired, and also as communication traffic increases, higher-efficiency communication is desired.
In multi-hop communication, a communication state at a relay target cannot be directly identified. Therefore, there is a possibility that communication cannot be performed due to a communication fault or other errors. When communication cannot be performed, a communication path is searched for. During the search for the communication path, communication is disconnected. Therefore, in order to perform highly reliable communication, ensuring a redundant path in advance has been proposed (see Patent Literature 1 listed below).
Meanwhile, in multi-hop communication, as a method for increasing the communication efficiency, the number of communication terminals is limited. With this method, a multi-hop network is managed hierarchically, and a communication path is constructed by communication terminals positioned at a higher hierarchy level. As a hierarchical management method, in hierarchical state routing (HSR) for example, an area is divided into several areas, and a representative node is located in each of the areas to reduce traffic for controlling a communication path and to therefore increase the communication efficiency (see Non Patent Literature 1 listed below).